Instrumented shoes, foot sensors, and gait analysis systems are present to a limited extent in published literature and the marketplace. Existing systems primarily consist of 1) simple activity sensors that give distance and rate of motion, 2) large and complex clinical systems suitable only for a laboratory, doctor's office, or shoe store, and 3) instrumented insoles.
Biomechanical motion has been analyzed in laboratory facilities using complex optical sensing systems and in medical offices with clinicians making visual qualitative observations of the subject's gait. Commercial technologies for plantar pressure assessment including the Emed Sensor Platform and Pedar Insole System by Novel Electronics, Inc., of St. Paul, Minn., United States; F-Scan System by Tekscan, Inc., of Boston, Mass. United States; and the Musgrave Footprint System by WM Automation and Preston Communication, Ltd., of North Wales, United Kingdom. In these technologies, a fine grain matrix array of sensors measures force when the foot contacts the sensor. Systems of this type are bulky, expensive and not practical for a consumer outside of a laboratory setting.
Prior art discrete in-shoe sensors located at designed anatomical points are obtrusive and irritating to a user, have edge effects between the sensor material and the surrounding insole, are subject to motion in the shoe resulting from shear stress, are subject to mechanical damage at the electrical connections, may be distorted by the contoured shape of the sole, and sensor performance may be affected by humidity and heat such that the recorded values may not accurately reflect the pressure experienced by these anatomical points in an un-instrumented shoe.
Researchers have used force-sensitive resistors (FSRs) at the five metatarsal heads, big toe, and heel in a tethered system for gait analysis, but the wires of such systems are unduly obtrusive and do not allow field testing. Examples include U.S. Pat. Nos. 5,899,963 and 6,122,960, issued to Hutchings et al.
Other researchers have pointed out the need for an inexpensive in-shoe system for gait analysis and utilized three orthogonal accelerometers, three orthogonal gyroscopes, four force-sensitive resistor plantar pressure sensors in a removable insole, two bend sensors, dynamic pressure sensors, and electric field height sensors. The objective of the GaitShoe was to 1) make no change in the gait, 2) characterize the motion of both feet, 3) be untethered, and 4) use the subjects' own shoes. In the GaitShoe, the FSRs were located at the medial (first) and lateral (fifth) metatarsal heads and medial and lateral sides of the heel pads. Radio-frequency (RF) transmission was used to send the data to a computer. U.S. Pat. No. 6,836,744, issued to Asphahani et al. (“Asphahani”), involves a similar system to the Gaitshoe. Asphahani also discloses sensors that are removable from a shoe.
U.S. Pre-Grant Publication No. 2011/0054359, by Sazonov et al. (“Sazonov”), discloses an activity sensor directed to weight-management applications. Sazonov discloses “A footwear system for monitoring weight, posture allocation, physical activity classification and energy expenditure” specifically comprising an accelerometer, pressure sensing device, and transmitter. In Sazonov, data from sensing device is sent wirelessly to a controlling device such as a smart phone. However, Sazonov discloses sending data to a controlling device in a burst mode so that the wireless network receiver and the transmitter can be powered off for a majority of time to reduce power consumption. For example, data is transmitted using a Bluetooth transceiver such as in the Nike+ Sport Sensor by Nike. Burst mode transmission involves data received by the receiver that is not synchronized with the sensor. If there are multiple sensors as between both a subject's feet or among multiple subjects, the data from each sensor is uncorrelated in time and, therefore, the data is not very useful for determining body mechanics.
The prior art discloses measuring pressure on the plantar surface of the foot using FSR, force sensitive capacitors, piezoelectric transducers, and other means. However, instrumented shoe systems beyond relatively simple pedometers are notably absent from the marketplace. In particular, it is believed that instrumented shoes for gaming applications are also absent from any literature. Rather, gaming applications have relied on external instrumented platforms such as the Nintendo Wii Fit Balance Board and Dance Dance Revolution's Dance Pad.
An FSR, as disclosed in U.S. Pat. No. 4,314,228, issued to Eventoff et al. (“Eventoff I”), which is hereby incorporated by reference in its entirety, is a device that measures force through the amount of contact between two parallel surfaces separated by an air gap produced by a spacer between the two surfaces imprinted in various patterns with a resistive semiconducting material conducting material. The greater the force between the surfaces, the more the air gap is closed, increasing the physical contact between the surfaces and decreasing the resistance of the device. In a thru mode FSR configuration, both substrates are printed with a connectorized conductive pad and overprinted with a semiconducting FSR material and faced toward each other separated by a spacer layer with a central hole so the conductivity is established by force between the two substrates. In a shunt mode FSR configuration, the FSR includes one substrate printed with a semiconducting FSR material, and a second layer imprinted with two connectorized sets of interdigitated electrodes separated by a spacer so the conductivity is established by force that increases the contact of the electrodes with the FSR layer thereby increasing the conductivity of one set of electrodes to the other through the semiconducting material. The three layers comprising a shunt mode design are shown in FIG. 1.
Dots of dielectric material may be placed on one surface or another to impede the surfaces from coming together. The air gap must be vented in some way to allow the two surfaces to come together. This, however, creates problems because the resistive characteristics of the commercial resistive materials, such as molybdenum disulfide, change with humidity. Thus, an FSR could be rendered completely inoperable by immersion in liquid, such as water.